write support

1 files changed, 31 insertions, 1 deletions

diff --git a/pkg/util/ref.go b/pkg/util/ref.go
index 69f7db4..05ef08f 100644
--- a/pkg/util/ref.go
+++ b/pkg/util/ref.go
@@ -1,6 +1,9 @@
 package util
 
 import (
+	"fmt"
+	"io"
+
 	"lukeshu.com/btrfs-tools/pkg/binstruct"
 )
 
@@ -8,8 +11,14 @@ type File[A ~int64] interface {
 	Name() string
 	Size() (A, error)
 	ReadAt(p []byte, off A) (n int, err error)
+	WriteAt(p []byte, off A) (n int, err error)
 }
 
+var (
+	_ io.WriterAt = File[int64](nil)
+	_ io.ReaderAt = File[int64](nil)
+)
+
 type Ref[A ~int64, T any] struct {
 	File File[A]
 	Addr A
@@ -22,7 +31,28 @@ func (r *Ref[A, T]) Read() error {
 	if _, err := r.File.ReadAt(buf, r.Addr); err != nil {
 		return err
 	}
-	if _, err := binstruct.Unmarshal(buf, &r.Data); err != nil {
+	n, err := binstruct.Unmarshal(buf, &r.Data)
+	if err != nil {
+		return err
+	}
+	if n != size {
+		return fmt.Errorf("util.Ref[%T].Read: left over data: read %d bytes but only consumed %d",
+			r.Data, size, n)
+	}
+	return nil
+}
+
+func (r *Ref[A, T]) Write() error {
+	size := binstruct.StaticSize(r.Data)
+	buf, err := binstruct.Marshal(r.Data)
+	if err != nil {
+		return err
+	}
+	if len(buf) != size {
+		return fmt.Errorf("util.Ref[%T].Write: expected to want to write %d bytes, but got %d bytes to write",
+			r.Data, size, len(buf))
+	}
+	if _, err = r.File.WriteAt(buf, r.Addr); err != nil {
 		return err
 	}
 	return nil